Sealing apparatus for electrical apparatus oil sampler and conditioner for solid state sensors

ABSTRACT

A gas monitoring apparatus and system that provides for reliable and accurate monitoring of gaseous hydrogen and other compounds in dielectric oil. The apparatus provides an environment for and is used in conjunction with metal oxide semiconductor sensors. Apparatus for creating a fluid-tight environment for the metal oxide semiconductor and a heating manifold are detailed.

FIELD OF THE INVENTION

The present invention relates to apparatus and methods for monitoringdissolved gases in liquid, and more particularly, the invention relatesto an apparatus and method for sampling and conditioning electricalinsulating oils so that gas dissolved in the insulating oils may bemonitored reliably by solid state sensors.

BACKGROUND OF THE INVENTION

The electric power industry has for many years recognized that thermaldecomposition of the oil and other insulating materials withinoil-insulated electrical apparatus can lead to the generation of anumber of “fault gases.” These phenomena occur in assets such as oilfilled transformers (both conservator and gas-blanketed types), load tapchangers, transformer windings, bushings and the like. The presence offault gases may be a measure of the condition of the equipment. As such,detection of the presence of specific fault gases in electricalapparatus, and quantification of those gases can be an important part ofa preventative maintenance program.

The presence of fault gases in oil-blanketed transformers withconservators and other utility assets has well documented implicationsrelating to the performance and operating safety of the transformer.There is a substantial body of knowledge available correlating thepresence of gases with certain, identified transformer conditions andfaults. It is therefore beneficial to monitor the condition ofdielectric fluids in electric equipment as a means to maximizeperformance, and at the same time minimize wear and tear on theequipment, and to thereby minimize maintenance costs and down time.Thus, information relating to the presence or absence of certain faultgases in transformer oil can lead to greatly increased efficiency in theoperation of the transformer.

As an example, it is known that the presence of certain fault gases intransformer oil can be indicative of transformer malfunctions, such asarcing, partial or coronal discharge. These conditions can cause mineraltransformer oils to decompose generating relatively large quantities oflow molecular weight hydrocarbons such as methane, in addition to somehigher molecular weight gases such as ethylene and acetylene, and alsohydrogen. Such compounds are highly volatile, and in some instances theymay accumulate in a transformer under relatively high pressure. This isa recipe for disaster. Left undetected or uncorrected, equipment faultscan lead to an increased rate of degradation, and even to catastrophicexplosion of the transformer. Transformer failure is a significantlyexpensive event for an electric utility, not only in terms of down timeand the costs of replacement equipment, but also in terms of the costsassociated with lost power transmission and dangers to workers andothers. On the other hand, by closely monitoring dissolved gases intransformer oil, the most efficient operating conditions for a giventransformer can be actively monitored and the transformer load may berun at or near its optimum peak. Moreover, when dangerous operatingconditions are detected the transformer can be taken off line formaintenance.

Despite the known need for reliable equipment to monitor gas in oil,designing equipment that holds up to the rigors of on-site conditionshas been problematic for a variety of reasons. That said, there are anumber of solutions known in the art. For example, mechanical/vacuum andmembrane extraction methods and apparatus for degassing transformer oilare well known, as exemplified by U.S. Pat. No. 5,659,126. This patentdiscloses a method of sampling headspace gas in an electricaltransformer, analyzing such gases according to a temperature andpressure dependent gas partition function, and based on the derivedanalysis predicting specific transformer faults.

An example of a gas extraction apparatus that relies upon a membranetube for extraction of gas from transformer oil is disclosed in U.S.Pat. No. 4,112,737. This patent depicts a plurality of hollow membranefibers, which are inserted directly into transformer oil in thetransformer housing. The material used for the membrane is impermeableto oil, but gases dissolved in the oil permeate through the membraneinto the hollow interior of the fibers. A portable analytical devicesuch as a gas chromatograph is temporarily connected to the probe sothat the test sample is swept from the extraction probe into theanalytical device for analysis.

Although these devices have provided benefits, there are numerouspractical problems remaining to the development of reliable apparatusfor extraction, monitoring and analysis of fault gases in transformeroils. Many of these problems relate to the design of reliable fluidrouting systems that are redundant enough to provide a relativelymaintenance free unit. Since transformers are often located inexceedingly harsh environmental conditions, fluid routing problems aremagnified. This is especially true given that the instruments needed toreliably analyze the gases are complex analytical instruments. Twopatents that describe the difficulties of these engineering challengesare U.S. Pat. Nos. 6,391,096 and 6,365,105, which are owned by theassignee of this invention and both of which are incorporated herein bythis reference. These two patents illustrate not only the complexitiesof the fluid routing systems needed, but solutions that have proved veryreliable. Moreover, many of the existing analytical devices rely uponconsumables such as compressed gasses, which increase the costs andmakes such devices suitable only for the largest and most expensiveutility assets.

One of the most critical points in the analytical process is theextraction apparatus, where gas is actually separated from theelectrical insulating oil. While there are several known apparatus foraccomplishing this task, experience has shown that the extractor is onepoint where failure can occur. Stated another way, extraction devices todate have been more fragile than desired and cannot fully withstand theextreme conditions that are routinely encountered in field applications.As a result, additional support equipment or operation constraints areadded to compensate for the performance shortcomings and to protect theextraction technology, which adds considerably to the cost. Despiteadvances in the technological solutions surrounding the extractiondevices, especially those described in the '096 and '105 patents, thereis a need for an extractor that is reliable and performs accuratelyunder all conditions for substantial lengths of time without beingmonitored.

Gas sensors such as chromatography and photo-acoustic spectroscopy thatare commonly used to analyze extracted gases are very complicated,expensive and as such are typically reserved for monitoring largetransformers were multiple gas analysis is cost effective in protectingexpensive assets.

For smaller transformers, simpler, lower cost, single gas sensors may beappropriate and sensors such as those described in U.S. Pat. Nos.5,279,795 and 7,249,490 which are incorporated herein by this reference,utilize a solid state sensor made from palladium-nickel. The problemwith these sensors is that they are very susceptible to oil and ambienttemperature variations and oil flow. In addition these monitors do nothave pumps to actively transport the oil sample over the sensor element.They rely on thermal cycling or diffusion, which greatly slows theirresponse time.

SUMMARY OF THE INVENTION

The advantages of the present invention are achieved in a firstpreferred and illustrated embodiment of a gas monitoring apparatus andsystem that provides for reliable and accurate monitoring of gaseoushydrogen and other compounds in dielectric oil. The apparatus providesan environment for and is used in conjunction with a hydrogen sensorassembly such as the metal oxide semiconductor sensors described in U.S.Pat. Nos. 5,279,795 and 7,249,490. The invention provides an environmentin which variations in oil temperature and ambient temperature areeliminated and to thereby insure that analytical data are not affectedby these environmental conditions. The invention further provides anenvironment in which variations in changes in oil flow over the sensorelement are eliminated in order to eliminate data irregularities thatare caused by oil flow dependencies. The invention provides improvedresponse time for obtaining data from the sensor because oil is activelymoved over the sensor element. The present invention also incorporates acalibration cycle during which the sensor element is calibrated.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood and its numerous objects andadvantages will be apparent by reference to the following detaileddescription of the invention when taken in conjunction with thefollowing drawings.

FIG. 1 is a schematic perspective view of an illustrated embodiment ofthe present invention attached to an oil-filled transformer asset.

FIG. 2 is a perspective view of one embodiment of the apparatus of thepresent invention shown in isolation and enclosed in a protectivehousing.

FIG. 3 is perspective and exploded view of the apparatus shown in FIG.2, illustrating the individual components.

FIG. 4 is a perspective and exploded view of selected components of theapparatus shown in FIG. 3, and specifically, the components of the oilpump and oil cooling section of the apparatus.

FIG. 5 is a perspective and exploded view of the components of the oilpump and oil cooling section shown in FIG. 4, taken from a differentpoint of view relative to FIG. 4.

FIG. 6 is a yet another perspective and exploded view of the oil pumpand oil cooling section of the apparatus shown in FIG. 3 from yetanother point of view.

FIG. 7 is a perspective and exploded view of selected components of thethermal conditioning section of the apparatus shown in FIG. 3.

FIG. 8 is yet another perspective and exploded view of selectedcomponents of the thermal conditioning section apparatus shown in FIG.3.

FIG. 8A is a perspective and exploded view of an alternative embodimentof the assembled heater manifold and sensor assembly that incorporates asealing system. In FIGS. 8A through 8D the heater manifold and sensorassembly are shown in isolation without adjacent components.

FIG. 8B is a cross sectional view of the exploded heater manifold andsensor assembly shown in FIG. 8A taken along the line 8B-8B of FIG. 8A.

FIG. 8C is a perspective view of the alternative embodiment of theassembled heater manifold and sensor assembly shown in FIGS. 8A and 8B,illustrating the components in an assembled condition.

FIG. 8D is a cross sectional view of the assembled heater manifold andsensor assembly shown in FIG. 8C taken along the line 8D-8D of FIG. 8C.

FIG. 9 is a perspective and relatively greater close up view of thethermal control assembly according to the present invention, showing thecomponents of the assembly in an assembled condition.

FIG. 10 is a perspective view similar to FIG. 9 of the thermal controlassembly but showing the assembly from a different point of view fromthe view of FIG. 9.

FIG. 11 is a perspective and close up view of selected components of thethermal control assembly.

FIG. 12 is a schematic fluid flow diagram showing the fluid flow pathsduring an optional calibration step.

DETAILED DESCRIPTION OF PREFERRED AND ILLUSTRATED EMBODIMENTS STRUCTURE

With reference to FIG. 1, apparatus and system 10 is illustratedschematically attached to an oil-drain port of an oil-filled electricaldevice (referred to at times as an “asset”), identified with referencenumber 1. It will be appreciated that the invention described herein maybe used with many different types of electrical devices, and also thatthe device may be attached to many different locations on the devices.The figures included herein are thus intended to be exemplary but notlimiting.

As detailed below, the system and apparatus 10 is comprised of a gassensing element with associated electronics and cabling, a fluiddelivery system to provide fresh samples to the gas sensing element, athermal control system for the sample fluid, a second thermal controlsystem for the gas sensing element electronics environment, andadditional electronics for data logging, communications, powerconditioning and alarming.

The apparatus 10 is intended for use on oil filled electrical utilityassets such as transformers and load tap changers. As noted above and asshown in FIG. 1, the apparatus 10 is mounted on the utility asset at avalve that accesses the insulating oil within the asset, typically amineral or ester oil. The system detects trace dissolved hydrogen in themineral oil and when either a fixed concentration threshold or a rate ofchange in the hydrogen concentration are exceeded, the system alarms toalert the utility of the hydrogen generation event. As hydrogen isgenerated in most transformer fault conditions, it is an excellentindicator of a developing fault within the transformer.

Generally described, the apparatus and system 10 functions by drawing afresh oil sample into a small internal volume containing the gas sensingelement. The oil sample is thermally conditioned to a pre-settemperature. When the desired temperature of the sample is achieved, thegas sensing element makes a measurement which is logged within thesystem. The gas sensing element and its associated electronics are verythermally sensitive. By controlling the thermal environments of thesecomponents, the precision, accuracy and reproducibility of the hydrogenreadings are greatly improved due to the diminishment of theinterferences from differences in temperature reading to reading, anddrift is minimized or eliminated.

Additionally, the apparatus and system 10 has a unique capability forcalibration. The fluid sample path can be optionally split so that thereare two possible sample supplies separated through 3-way valves on theoil inlet and outlet. Both sample paths would be connected to the commonoil paths to and from the utility asset. The primary fluid path woulddeliver oil from the utility asset for standard analysis. The secondarysample path would have an incorporated membrane located between the3-way sample selection valves. A compressed gas standard could beapplied to the gas side of the membrane, which would inoculate andequilibrate with the isolated oil in the secondary sample path. Whensystem calibration is necessary, the secondary sample path would beactivated so that the inoculated oil would be introduced into the sensorenvironment. Excess inoculated oil would be flushed back to the utilityasset with fresh oil from the utility asset replenishing the secondarysample path for isolated inoculation. The gas on the gas side of themembrane on the secondary sample path could also be atmospheric air.This would effectively generate a “zero” gas standard devoid of the gasof interest.

Turning now to FIGS. 2 through 10, the basic components of the apparatusand system 10 will be described. Apparatus and system 10 includes threeprimary sections or systems, each of which comprises multiple componentsand each of which is detailed herein: an electrical oil cooling andtransport pump section 14, a thermal conditioning section 30, and acontrol system 100.

With reference to FIG. 2, apparatus 10 includes a threaded adaptor 12that connects to a threaded port in the electrical asset 1 and which isadapted to receive electrical oil from the asset. An electrical oilcooling and transport pump section is shown generally with referencenumber 14. The cooling and transport pump section 14 includes a firstinsulation plate 16, a heat sink 18, a second insulation plate 20, allof which are attached to a cold manifold housing 22 with appropriatefasteners such as screws 24. A motor mount 26 is mounted at a top end ofthe manifold housing 22 and serves as the mount for a stepper motor 28.Heat sink 18 defines a passive cooling manifold that helps to withdrawheat from the fluid from asset 1.

A thermally controlled heating section, identified generally withreference number 30 is mounted to the electrical oil cooling andtransport pump section 14. Within the multiple components contained inthe thermal conditioning section are individual systems, such as thermalcontrol apparatus 61, which itself comprises multiple individualcomponents and systems including a first thermal zone 65 and a secondthermal zone 67, all of which are detailed below. The thermalconditioning section 30 includes an external housing 34 that enclosesthe components described below. The entire apparatus 10 includesappropriate gaskets and seals to insure a fluid-tight environment.

The optimal performance (consistent precision, accuracy andreproducibility with lowest drift) and life of the sensor assembly 70 isachieved by operating the sensor assembly and its associated analogelectronics isothermally, but at two different temperatures. Thisrequires the implementation of first and second distinct and separatethermally controlled zones for the sensor and analog electronics—firstand second thermal zones 65 and 67. The first thermally controlled zone65 is operable to control the thermal conditions associated with thesensor assembly 70; the second thermally controlled zone 67 is operableto control the thermal conditions associated with the analog electronicsthat control and operate with the sensor assembly 70. Each of thethermally controlled zones 65 and 67 is independently controllable for“heating” and separately for “cooling”, as conditions dictate, and eachis thermally isolated from the other and from other components of theapparatus 10 and from the ambient environment.

Additionally, the optimal control temperatures for the sensor assembly70 and the analog electronics are at or below the maximum operating oiland ambient temperatures required for the system 10 based upon thesensor assembly 70 technology. As such, in addition to first and secondpulse width modulated heater controls, system 10 incorporates two pulsewidth modulation controlled Peltier thermoelectric coolers (TEC) toprovide continued thermal control at the highest and lowestenvironmental exposure requirements. The thermoelectric coolers are usedto cool the sensor and analog electronic zones for high environmentaltemperature exposures. For low environmental temperature exposures, thecurrent applied to the thermoelectric coolers is reversed to apply aheating assist to the heater control systems for each of the thermalzones. Therefore, as described in detail below, system 10 utilizes twothermally controlled zones with a total of six thermal control systems,two heater controls, two cooler controls and two controls for operatingthe TECs in the reverse direction as heater assists.

The entire apparatus and system 10 including the electrical oil coolingand transport pump section 14 and thermal conditioning section 30 isshown in exploded view in FIG. 3. Electrical oil cooling and transportpump section 14 includes a worm gear drive assembly 40 that is driven bystepper motor 28 and which is configured for precisely controlling flowof fluid through apparatus 10. Although not described in great detail,but as shown in FIGS. 4 and 5, worm drive gear assembly 40 includesappropriate gearing and sealing components to insure a fluid-tight andleak-free environment and defines a precisely controllable metering pumpfor controlling flow of oil through apparatus 10. As detailed below,apparatus 10 includes porting that defines fluid flow paths of aliquotsof oil from the reservoir of oil in asset 1 through the apparatus 10,specifically, from asset 1 into electrical oil cooling and transportpump section 14, then into thermal conditioning section 30, and morespecifically, sensor 70, and back to asset 1.

Returning to FIG. 3, the fluid sample flow path is shown schematically.Specifically, cooling heat sink 18 is mounted to adaptor 16 and includesa sample core tube 80 that defines an inlet for fluid from asset 1, andas described below, functions as a cooling chamber for oil received fromasset 1. An oil inlet path 82 defines fluid flow routing into coldmanifold housing 22, and as more specifically described below, into theworm gear chamber within the housing 22. The oil inlet path continuesfrom housing 22 through appropriate porting such as insulating tubes 86and 87 to heater manifold 60, and as more specifically described below,into a chamber in the heater manifold that houses sensor assembly 70. Anoil return path 84 is defined by appropriate porting from the chamber inthe heater manifold 60, through cold manifold housing 22, and back intoasset 1. In order to maintain thermal isolation of oil, insulating tubes86 and 87 are preferably nylon because of its thermal efficiency andbecause it minimizes transfer of heat from the tubing to surroundingcomponents.

The cold manifold housing 22 is shown in isolation in FIG. 6. Worm drivegear assembly 40 includes a pair of worm gears 42 and 44 with oppositespiral windings that are driven by stepper motor 28 and which are housedin a worm gear chamber 46 in the manifold housing 22. When worm gears 42and 44 are in the operable positions in cold manifold housing 22, theopposed spiral windings intermesh to define a portion of the oil flowpath over the intermeshed windings. Oil inlet path 82 leads into wormgear chamber 46 and operation of worm gears 42 and 44 by stepper motor28 causes controlled and known volumes of fluid to flow through theinlet path into heater manifold 60.

Beginning with the components immediately adjacent electrical oilcooling and transport pump section 14, thermal conditioning section 30includes a plate 50 between gasket 32 and the cold manifold housing 22.Plate 50 is a metallic plate that serves as a supporting structure forcomponents of electrical oil cooling and transport pump section 14 andthermal conditioning section 30, and for purposes of this description ofthe invention, effectively separates the cooling side from the hot side.Plate 50 includes a pair of heat sinks 51 attached to the plate on theside of the plate that faces electrical oil cooling and transport pumpsection 14. Plural insulating blocks 52 are incorporated in the heatingsection in order to thermally insulate and isolate a heater manifold 60,which is a relatively massive, preferably monolithic block of a metalsuch as aluminum that has excellent heat transfer properties, and whichis heated with resistive heating elements that are attached to a printedcircuit board 74 that is a component of the thermal control assembly 61.The insulating blocks are preferably urethane foam, but numerousmaterials may be utilized for the thermal insulation properties. Heatermanifold 60 has an internal chamber 90 (FIG. 7) that houses the sensorassembly 70 and the sensor assembly is retained in the chamber 90 with abracket 71 that threads into bores in the manifold 60. Sensor assembly70 includes the electronics that define the gas sensors, and will beunderstood to be of the type described in U.S. Pat. Nos. 5,279,795 and7,249,490. The sensor assembly 70 is electrically connected to circuitboard 62 with a flex circuit 72.

Thermal conditioning section 30 comprises four separate printed circuitboards, each of which contains operational firmware and electronics forcontrol of apparatus 10 and for facilitating networked communicationscapabilities for the apparatus and system, and all of which comprisecontrol system 100. With reference to the figures, the four circuitboards are identified as first heater board 74, second heater board 77,analog sensor board 62 and main control board 101. Critical functions ofeach are detailed below.

Both of the first and second thermally controlled zones are located inthe thermal control assembly shown generally with reference number 61.

As shown in the exploded view of FIG. 7, the components of the thermalconditioning section 30 are sandwiched together and when assembled areretained in the housing 34. The plural insulating blocks 52 define aninsulation barrier that entirely surrounds the components of the thermalcontrol assembly 61 and effectively thermally isolates all components ofthe assembly. Beginning on the left hand side of FIG. 7 and generallymoving toward the right hand side, and omitting mention of theinsulation blocks, thermal conditioning section 30 begins with plate 50and includes a thermal control assembly 61, which comprises a heatermanifold 60, which includes (schematically) the oil inlet flow path 82from worm gear chamber 46, and the oil return path 84, which runs fromthe heater manifold 60 back to asset 1. Heater manifold 60 includes achamber 90 that is sized to receive sensor assembly 70, which as notedis electrically connected to circuit board 62 with flex circuit 72 andwhich is retained in the chamber with a bracket 71. Heater manifold 60is a block of metal such as aluminum that is heated by a pair ofresistive heating elements 92 (only one of which is shown in theperspective view of FIG. 7) that are mounted to first heater board 74and which are received in openings or slots 94 in heater manifold 60.Openings 94 are located on either side of chamber 90 and include attheir inner end thermal pads onto which the resistive heating elementsthat are pressed in the assembled unit, but which are not visible in theperspective views of the drawings. The slots 94 are arranged on eithersides of the location in manifold 60 where sensor 70 resides in themanifold so that the heating elements are arranged in close proximity tothe sensor 70 in the manifold 60. A temperature sensor 95 is provided onmanifold 60 between the two slots 94. Oil inlet flow path 82 and oilreturn flow path 84 both open into chamber 90, the inlet flow pathdefining the delivery path for aliquots of oil flowing into the sensorassembly 70 within chamber 90 and the oil flow return path 84 definingthe flow path for aliquots of oil flowing from the sensor assembly andultimately back to asset 1.

Sensor assembly 70 includes ports 96 (one of which is shown in FIG. 8)that define oil flow paths through which oil enters and escapes thesensor assembly. The solid state circuitry that defines the gasdetection functionality of the sensor assembly are contained within theassembly 70.

As noted above, it is important to insure that all connections andfittings are sealed so that there are no leaks in the system andapparatus 10. Any leaking oil will result in erroneous data. One of themost critical locations for a leak-free and fluid-tight environment isin heater manifold 60 and with sensor assembly 70 that resides inchamber 90 in the manifold. With reference to FIGS. 8A through 8D, asealing apparatus is detailed that provides a completely leak-freeenvironment for the manifold 60 and the sensor assembly 70. Withreference first to FIGS. 8A and 8B, the heater manifold 60 and sensorassembly 70 are shown in isolation in a perspective and exploded view.The upper surface 150 of heater manifold 60 has a recessed area 152 thatsurrounds the opening into chamber 90. An annular ledge 154 is formed inchamber 90 so that there is an upper chamber portion 156 that has agreater diameter than a lower chamber portion 158. The sensor assembly70 includes a sensor housing 160 that has an O-ring 162 in an O-ringgroove 164 near the “upper” end of the sensor housing 160. It will beappreciated that the electronic circuitry that defines the sensorportion of sensor assembly 70 is retained within the sensor housing 160and that oil flows into and out of the housing to expose the electroniccircuitry to the oil, as detailed elsewhere.

When sensor assembly 70 is inserted into chamber 90—i.e., with thesensor housing 160 inserted into the chamber—the O-ring 162 rests onledge 154, as best seen in FIG. 8D. A clamp ring 166 has an outerdiameter that is slightly less than the inner diameter of chamber 90 atupper chamber portion 156 and an inner diameter that allows the clampring to slide over the upper portion of the sensor housing 160. Statedanother way, with the sensor assembly 70 inserted into chamber 90, clampring 166 is inserted into upper chamber portion 156 such that the inneredge 168 of the clamp ring bears against O-ring 162 and such that theouter edge 170 of the clamp ring is above the level of surface 174 ofthe recessed area 152.

With the clamp ring 166 thus assembled with heater manifold 60 andsensor assembly 70, a retaining plate 176 which is sized to fit intorecessed area 152 is attached to the heater manifold 60 with four screws178, which thread into threaded openings 180 in the heater manifold. Theretaining plate 176 includes a central opening 182 that is smaller indiameter than clamp ring 166 but larger in diameter than the uppermostend of sensor housing 160. The retaining plate also has a slot 184through which flex circuit 72 may be inserted. The retaining platetherefore makes contact with the clamp ring but not the sensor housing.Since the outer edge 170 of the clamp ring 166 is above the level ofsurface 174, as the screws 178 are tightened the retaining plate 176 isdrawn toward the heater manifold in recessed area 152. As this happens,the retaining plate pushes the clamp ring downwardly, heater manifold 60to thereby compress the inner edge 168 of the clamp ring against theO-ring 166, which as noted above rests on ledge 154.

The compression of the O-ring 162 between the ring clamp 166 and theledge 154 defines a completely leak-free connection between the sensorassembly 70 and the heater manifold 60.

In FIGS. 9 and 10 the thermal control system 61 is shown in isolationand in an assembled condition with all insulating blocks 52 removed inorder to show the orientation of the various components. Beginning withFIG. 9, the components of thermal control system 61 are attacheddirectly to the side of plate 50 that faces the thermal conditioningsection 30—that is, the side of plate 50 opposite heat sinks 51. Asnoted, thermal control system 61 comprises first and second thermalzones 65 and 67. The first thermal control zone 65 is configured forheating and/or cooling the sensor 70 by heating and cooling manifold 60into which the sensor 70 is retained, and will be described first.

First thermal zone 65 comprises generally the following essentialcomponents:

Heater manifold 60;

heat transfer block 110;

first heater board 74; and

TEC 112.

Heater manifold 60 is mounted to plate 50 on plural stand-offs 63 thatmount the manifold in a spaced apart relationship with the plate 50, asshown. The oil inlet path 82 into manifold 60 and the oil outlet path 84are shown schematically. Heat transfer block 110 is mounted to plate 50with a thermal pad 116 between the mounting surface of the transferblock 110 and the plate. The heat transfer block is preferably arelatively massive structure fabricated from a metal such as aluminumthat has excellent thermal transfer qualities. A first facing surface ofTEC 112 is mounted to the inner-facing surface 120 of heat transferblock 110 that faces toward manifold 60; the opposite surface of TEC 112abuts and is directly attached to manifold 60. A TEC strap 114 extendsacross heat transfer block 110 and screws 122 extend through the strap114 and thread into threaded bores in manifold 60. When screws 122 aretightened, TEC 112 is tightly sandwiched between the heat transfer block110 on one side, and the manifold 60 on the opposite side of the TEC112. More specifically, the first facing surface of TEC 112 is pressedagainst heat transfer block 110 and the opposite facing surface ispressed against manifold 60. In addition to use of strap 114, or as analternative to the strap, an adhesive having good thermal transferqualities may be used to bond these sandwiched parts together. Theabutting relationship and close association of the TEC between themanifold and the heat transfer block insures excellent heat transferbetween these components. TEC 112 is electrically connected to secondheater board 77 and is controlled by the electronic control systemsassociated therewith.

The nominally “cold” side of TEC 112 faces and abuts manifold 60 and thenominally “hot” side of TEC 112 faces and abuts heat transfer block 110.As noted, however, since TEC 112 is a Peltier device the direction ofheat transfer may be reversed by reversing polarity of the currentthrough the TEC.

First heater board 74 is mounted directly to manifold 60 so that the tworesistive heating elements 92 are held in slots 94 with the heatingelements pressing against the pads contained in the slots.

Stand offs 160 are arranged at roughly the four corners of first heaterboard 74 and support in a spaced apart relationship from first heaterboard 74 a metal plate 164. Mounted below metal plate 164 and in anabutting relationship thereto is a thermal pad 166. Below thermal pad166 and spaced apart between both the thermal pad 166 and first heaterboard 74 is second heater board 77. A second thermal pad 168 is attacheddirectly to the outer-facing surface of metal plate 164 and the analogsensor board 62 is mounted to the second thermal pad 168.

The second thermal zone, shown generally at 67 in FIG. 10 is configuredfor heating and/or cooling the analog electronics that control sensor70, and specifically, the analog electronics associated with analogsensor board 62. The second thermal zone 67 is independently operatedfrom the first thermal zone 65 described above and is thermally isolatedtherefrom.

Second thermal zone 67 comprises generally the following components:

heat transfer block 150;

TEC 152;

TEC heat transfer bracket 154;

Heat transfer block 150 is mounted to plate 50 with a thermal pad 151therebetween. As with heat transfer block 110 the heat transfer block150 is preferably a relatively massive metal such as aluminum that hasexcellent thermal transfer qualities. One facing surface of TEC 152 ismounted to the surface 161 of heat transfer block 150 that faces towardmanifold 60; however, the TEC 152 is not in contact with the manifold 60and is spaced apart therefrom. TEC heat transfer bracket 154 is ametallic, roughly L-shaped member that is mounted to the opposite facingsurface of TEC 152. TEC heat transfer bracket 154 is in turn attached tometal plate 158, which lies between thermal pads 164 and 166. A TECstrap 156 extends across heat transfer block 150 and screws 168 extendthrough the strap and thread into bores in TEC heat transfer bracket154. When screws 168 are tightened, TEC 152 is tightly sandwichedbetween heat transfer block 150 and TEC heat transfer bracket 154 with amajor surface of the bracket 154 pressed against the TEC 152. As above;an adhesive with good thermal transfer qualities may be used to bondthese sandwiched parts together, either in combination with strap 156 oras an alternate thereto. The close association of the TEC 152 with theheat transfer block and the heat transfer bracket insures excellent heattransfer between the components and into metal plate 164. TEC 152 iselectrically connected to second heater board 77 and is controlled bythe electronic control systems associated therewith.

The nominally “cold” side of TEC 152 faces and abuts TEC heat transferbracket 154 and the nominally “hot” side of TEC 152 faces and abuts heattransfer block 150, but again, the direction of heat transfer throughthe TEC may be reversed by reversing polarity of the current. It will beappreciated that since both TEC 112 and 152 are capable of both heatingand cooling depending upon the direction of polarity of the appliedcurrent, these components are best referred to in a general sense asthermal conditioning modules. Moreover, use of the resistive heatingelements 92 may be considered optional given the ability of the TECs toheat and cool. Stated another way, depending upon specific environmentalconditions the resistive heating elements 92 may be omitted altogether,or alternately, not utilized by control (i.e., not powered) by controlsystem 100.

FIG. 11 is a relatively close-up view that illustrates the structuralassociations of selected components described above.

The entire apparatus and system 10 are under the control of a controlsystem 100, shown schematically in FIG. 1, and which preferably includestelephony and networking capabilities. Each of the circuit boards inapparatus 10 comprises a component of the control system 100. As notedabove, the control system 100 comprises firmware and electronics on fourseparate printed circuit boards: first heater board 74; second heaterboard 77; analog sensor board 62; and main control board 101; each ofthe boards 74. 77 and 62 are under the control of the main control board101.

Operation

As noted, operation of apparatus and system 10 is under the control ofcontrol system 100.

Worm gear assembly 40 defines a metering pump that is capable of causingflow of precise volumes of oil from the reservoir defined by asset 1 andthrough apparatus 10. Initially, stepper motor 28 is operated to drivethe worm gears 42 and 44 of worm gear assembly 40 to draw a quantity ofoil into the cooling chamber defined by tube 80, which as noted above ispart of heat sink 18, from the asset 1. Typically, the oil at this pointhas a relatively elevated temperature—it is thus referred to as being“hot.” The hot oil resides in the cooling chamber of tube 80 for aperiod of time sufficient for the oil to cool, via the ambient airaround heat sink 18. Apparatus and system 10 includes appropriatetemperature sensing capabilities, such as thermocouples and the likeconnected to control system 100.

The stepper motor 28 is then operated to cause the sample of cooled oilto flow into the thermal conditioning section 30, and more specifically,through oil inlet flow path 82 into chamber 90 of heater manifold 60,and thus into ports 96 of sensor assembly 70. Stepper motor 28 isdeactivated so that all oil flow in apparatus 10 ceases. The resistiveheating elements 92 are powered and the heater manifold is thus heated.Heating of heater manifold 60 continues and the oil is thus heated inchamber 90. The oil is allowed to reside in chamber 90 until the oil hasreached the pre-determined steady state oven temperature as determinedby temperature sensor 95. The gas sensor assembly 70 is then read bycontrol system 100 in a steady state temperature, with the oil stagnateand not flowing over or through the sensor assembly 70, which creates amuch more stable environment in which the sensor assembly may determinethe concentration of dissolved gas.

Once the analysis is complete, stepper motor 28 may be again activatedto cause the aliquot from chamber 90 to flow through oil return flowpath 84 and ultimately return to asset 1.

Analytical data from sensor assembly 70 is analyzed by appropriatetechniques by control system 100, either locally or remotely, and thedata are monitored.

It will be appreciated that the foregoing description of the operationcontemplates a “stop flow” operation where analysis is undertaken in azero fluid flow condition. The apparatus 10 is just as amenable toperforming analysis with equal precision, reliability and control underlow flow operating conditions. In a low flow analysis scheme, thermalcontrol systems can achieve thermal control of the sample under low flowconditions where the thermal characteristics of the oil can beadequately manipulated by the pulse width modulation control. Control ofthe rate of flow is necessary, as if the flow is too high, thermalcontrol can be lost. However, in that case it is only necessary that afresh and representative sample of fluid be delivered to the sensor.

Calibration

As noted previously, the apparatus and system 10 has a capability forcalibration. With reference now to FIG. 8, a calibration routine 100 isshown to include an inlet flow path 92 and return flow path 84. As shownin calibration routine 100 the fluid flow paths 82 and 84 can beoptionally split so that there are two possible sample suppliesseparated through a pair 3-way valves, 102 in the inlet flow path 82,and 104 in the outlet flow path 84.

In a first state condition, referred to as the analysis state, the inletand outlet fluid flow paths 82 and 84 are as described above. Thus,three way valves 102 and 104, which are under control of control system100, are set so fluid flows through from asset 1 through valve 102through worm gear drive assembly 40, to sensor assembly 70, as detailedabove. In the analysis state, oil from sensor assembly 70 flows throughflow path 84 and valve 104 back to asset 1.

In the second state condition, called the calibration state, valve 104is operated to divert the flow of oil from flow path 84 to a calibrationflow path 106, which flows through a calibration module 108. Calibrationmodule 108 includes a semi-permeable membrane that is exposed to air orcalibration gas on one side, and to the oil on the opposite side. Themembrane is permeable to gas but not oil. In the calibration state, oilflows into the calibration module and then the worm gear drive assemblyis stopped so that oil in the calibration module is allowed toequilibrate across the semi-permeable membrane with the referencegas—i.e., either air or a calibration gas.

In this instance, since the calibration cycle is relatively long theapparatus 10 may be routinely doing analyses while the trapped oilsample equilibrates with the calibration gas. When calibration is calledfor, the valves would be switched and the calibration gas inoculated oilwould be introduced into the sensor region of the device. Thiscalibration scheme would require the stopped flow operation.

A calibration loop 100 isolates the calibration gas from the fluid flowpathways 82 and 84. Specifically, a valve upstream of the calibrationmodule (under the control of control system 100) is plumbed in thecalibration gas line, which connects to the calibration module 108. Avacuum pump 114 is connected to the gas side of the membrane in module108 and is operable to move calibration gas (including air, if air isbeing used as the calibration gas) into and out of the module 108. Thecalibration gas is flushed to atmosphere, and this avoids returning anyfault gasses back to the asset 1. Thus, a calibration gas or air isdrawn into the calibration module 108 on the gas side of the membrane byopening valve 112 and operation of pump 114. The oil is held in thecalibration module 108 until equilibrium occurs byequilibration/inoculation of the gas from the gas side of the membranewith the oil on the oil side of the membrane. Valve 102 is then operatedso that the equilibrated oil flows from calibration module 108 throughflow path 106, through valve 102 and back to sensor assembly 70. Whenthe equilibrated oil is resident in sensor assembly 70, the gas issampled by the sensor element and the apparatus 10 is the calibrated.

Excess equilibrated/inoculated oil is flushed back to the asset 1 withfresh oil from the utility asset replenishing the secondary calibrationpath 106 for isolated inoculation. As noted, the gas on the gas side ofthe membrane on the secondary sample path could also be atmospheric air,which would effectively generate a “zero” gas standard devoid of the gasof interest.

Once calibration is done, valves 102 and 104 are returned to theanalysis state operations. Calibration is conducted at regularintervals, or as necessary.

In view of the many possible embodiments to which the principles of ourinvention may be applied, it should be recognized that the detailedembodiments are illustrative only and should not be taken as limitingthe scope of the invention. Rather, we claim as our invention all suchembodiments as may come within the scope and spirit of the claims of theinvention and equivalents thereto.

The invention claimed is:
 1. Sealing apparatus for creating a leak-freeenvironment for a gas sensor used for analysis of insulating oil fromelectrical assets, comprising: a manifold having a cylindrical chamberformed therein for receiving a gas sensor, said chamber having an upperportion having a first diameter and a lower portion with a seconddiameter that is less than the first diameter and an inwardly projectingannular ledge between the upper and lower portions; a gas sensor havinga cylindrical sensor body, said sensor body inserted into the chamber;an O-ring on the sensor body, said O-ring having an outer diameter thatis greater than the second diameter and less than the first diameter sothat when said O-ring is inserted into the chamber the O-ring contactsthe annular ledge; a clamp ring having an outer diameter that is lessthan the first diameter, said clamp ring encircling the sensor body andinserted into the upper portion of the chamber such that a lower edge ofsaid clamp ring contacts the O-ring; a retaining plate attached to themanifold and in contact with the clamp ring, said retaining platecompressed against said clamp ring to thereby compress the O-ring. 2.The sealing apparatus according to claim 1 wherein the retaining platehas a cylindrical opening with a diameter greater than the diameter ofthe sensor body and less than the outer diameter of the clamp ring. 3.The sealing apparatus according to claim 2 wherein an upper portion ofthe sensor body is received in the retaining plate cylindrical openingwhen the retaining plate is attached to the manifold.
 4. The sealingapparatus according to claim 3 wherein the retaining plate is in contactwith the clamp ring when the retaining plate is attached to themanifold.
 5. The sealing apparatus according to claim 4 wherein theO-ring is compressed between the annular ledge and the clamp ring whenthe retaining plate is attached to the manifold.
 6. The sealingapparatus according to claim 2 wherein the retaining plate has a slotformed therein extending from the cylindrical opening to an edge of theretaining plate.
 7. The sealing apparatus according to claim 1 whereinthe sensor body has an upper surface and the manifold has an uppersurface surrounding the chamber, and wherein in a first uncompressedcondition the upper surface of the sensor body is positioned above theupper surface of the manifold surrounding the chamber.
 8. The sealingapparatus according to claim 7 wherein the manifold further defines arecessed seat, and wherein in a second compressed condition theretaining plate is received in the recessed seat.
 9. The sealingapparatus according to claim 8 including at least one heating elementfor heating the manifold.